Zoo officials said visitors reported seeing the adult attack the nearly 4-month-old female infant around 3:45 p.m. However, workers could not stop the attack because it is not safe for them to occupy the same space as the chimpanzees, said Jason Jacobs, a zoo spokesman. About 60 visitors witnessed the attack.

"One of the males took the baby away and kind of a fight ensued and a ruckus as the females were trying to get the baby back, and that baby ended up being killed," said Jennie Becker of the Los Angeles Zoo.

The unnamed baby chimp's mother, Gracie, "has proved to be a caring mother," Jacobs said in a statement, and "there was no indication of aggressive behavior towards the infant" from other members of the chimp troop.

The baby was the first chimp born at the zoo in 13 years.

"Chimpanzee behavior can sometimes be aggressive and violent, and the zoo is sorry that visitors had to be exposed to this," Jacobs said. "This is a heartbreaking and tragic loss for the zoo and especially for the Great Ape Team who have worked diligently to care for the infant and its mother since its birth."

Jacobs said Gracie and the baby's grandmother would be allowed to keep the infant overnight to allow them to grieve. The body will be removed Wednesday morning.